The present invention relates to a control system for a plant, and more particularly to a control system that identifies model parameters of a controlled object model which is obtained by modeling the plant, and includes a controller for controlling the plant using the identified model parameters.
There has been known a control system that identifies model parameters of a controlled object model which is obtained by modeling a plant which is a controlled object, and includes a controller for controlling the plant using the identified model parameters (Japanese Patent Laid-open No. 2000-297679, for example). This control system includes a model parameter identifier for identifying the model parameters on a real-time basis, and controls the plant using the identified model parameters.
The model parameter identifier detects an identifying error which is a difference between an output of the plant, which is calculated using the identified model parameters, and an actual output of the plant. Further, the model parameter identifier corrects the model parameters in order to eliminate the identifying error. Therefore, regarding the model parameter identifier, the following problems may occur.
Due to nonlinear characteristics and disturbance whose average value is not “0”, the identifying error does not become “0” even though substantially optimum model parameters have actually been obtained. Therefore, the model parameters which do not need to be corrected are occasionally corrected. As a result, a drift of the model parameters, which is apt to occur when the input and output of the plant is maintaining a substantially constant value, occurs to make the control performed by the controller unstable.